The present invention relates to a method of, and a die for, extruding a catalyst, a catalyst precursor, or a catalyst support. The method is suitable in a process for manufacturing a catalyst, catalyst precursor, or a catalyst support for use in a multitubular fixed bed reactor. The method is particularly but not exclusively suitable in a process for manufacturing a catalyst, catalyst precursor, or a catalyst support for use in a Fischer-Tropsch process.
The Fischer-Tropsch process can be used for the conversion of synthesis gas (from hydrocarbonaceous feed stocks) into liquid and/or solid hydrocarbons. Generally, the feed stock (e.g. natural gas, associated gas and/or coal-bed methane, heavy and/or residual oil fractions, coal, biomass) is converted in a first step into a mixture of hydrogen and carbon monoxide (this mixture is often referred to as synthesis gas or syngas). The synthesis gas is then fed into one or more reactors where it is converted in one or more steps over a suitable catalyst at elevated temperature and pressure into mainly paraffinic compounds ranging from methane to high molecular weight modules comprising up to 200 carbon atoms, or, under particular circumstances, even more. Preferably the amount of C5+ hydrocarbons produced is maximized and the amount of methane and carbon dioxide is minimized.
Fischer-Tropsch catalysts are known in the art, and frequently comprise, as the catalytically active component, a metal from Group VIII of the Periodic Table. (References herein to the Periodic Table relate to the previous IUPAC version of the Periodic Table of Elements such as that described in the 68th Edition of the Handbook of Chemistry and Physics (CPC Press)). Particular catalytically active metals include ruthenium, iron, cobalt and nickel. Cobalt is a preferred catalytically active metal. The catalytically active metal is preferably supported on a porous catalyst support. The porous catalyst support may be selected from any of the suitable refractory metal oxides or silicates or combinations thereof known in the art. Particular examples of preferred porous catalyst supports include silica, alumina, titania, zirconia, ceria, gallia and mixtures thereof, especially silica and titania. A process for the preparation of such catalysts is described in EP 1 042 067.
One way of producing a catalyst precursor, a catalyst, or a catalyst support for a multitubular fixed bed reactor is to feed a paste comprising a support material and optionally a catalytically active component or a precursor thereof from a hopper into an extruder. In case the extrusion is part of a method in which a Fischer Tropsch catalyst is produced, the paste may comprise a catalytically active metal and/or a promoter. A number of dies at the end of the extruder each comprise a plurality of small apertures through which the paste is forced. The resulting extrudate is an elongated catalyst precursor, catalyst, or catalyst support suitable for use in a fixed bed multitubular reactor.
The catalyst used in such a multitubular reactor is limited by mass transfer and so maximizing its external surface area is preferred. Therefore a variety of shapes may be produced by the dies to maximize external surface area and minimize the pressure drop in the reactor. EP 0 510 770 describes the production of a helical trilobed extrudate and an extended trilobe shape is disclosed in WO/03/103833. WO2004/041430 describes particles with an elongated cross section.
Extrusions aimed at forming relatively small and alternative shapes make high demands upon the extrudability of the extrusion mix, which can be optimized by varying the liquid content, and/or application of extrusion aids, for instance methylcellulose.